Part one

Stepping motor basics

A hybrid stepping motor is a type of synchronous motor, brushless permanent magnet using laminated steel or soft iron pole pieces. Include teeth well distributed around the stator and rotor to create a multi polar machine (usually 50 or 100 posts.) The multitude of magnetic poles acts as a torque multiplier and, simultaneously, a speed limiter. To further increase torque, the air gap between stator and rotor is extremely small, the smallest of any electric motor, with a typical separation of 0.002-in. or 0.05 mm. This rotor smallest mechanical clearances between the stator and the movement makes the hybrid stepping motor without protection, especially suggestible to the effects of moisture induced corrosion.

Corrosion can be a problem for all types of electric motors. Moisture and oxidation can lead to electrical shorts, with failure or overheating. The problems of other types of motor with moisture and other corrosion, stepping motor are particularly susceptible to blockage of the rotor. This is due to extremely small air gaps needed to create these high-torque. Even a small amount of corrosion can bring the gap between the stator and rotor, and locking the parts together, and then the stepping motor stops moving. The hybrid stepping motors work best at speeds below 1,000 rpm, and has more consecutive pair of equivalent size brushless motors common. The motor operates in precise steps that are called. For example, 50 poles, two-phase hybrid 1.8° stepping motor achieves a magnitude in full step by step movement, while the 0.9° stepping motor 100 pin reaches in all its magnitude step by step movement.

Test coatings

Verification of implementation corrosion resistant coatings involved review of the new atmosphere of salt, or sprinkle the tests used widely by industry and defense industries. MIL-STD-202G, 101E test method, is an all-purpose accelerated corrosion test, and the toughest test of corrosion for commercial and industrial applications. Although it is a military standard, is still effective for commercial and industrial applications, a notable difference is the absence of any height requirement. This form of corrosion test and the procedure was applied to evaluate the corrosion testing capabilities with a major change. The test reached 140 hours of testing without interruption. This condition is higher than all defined test conditions, except one used primarily by industry self-defense.

The test was carried out by two stepping motors treated and untreated. After 40 hours of salt spray test of a stepping motor is not treated, the untreated motor was removed from the test chamber and full of energy and not to operate. The main reason for failure was corrosion (rust) between the stator and rotor.

The stepping motor corrosion-proof coating, showed no formation of corrosion after 140 hours exposure to salt test equivalent. In other words, after the corrosion test, the stepping motors are performance tested and works successfully.


The corrosion test successfully demonstrated the new design technique can help layer the stepping motor to work harder and better.